1. Field of the Invention
The present invention relates to wide angle video display apparatus. In particular, the present invention relates to display apparatus wherein a visual scene is projected onto a retroreflective surface from a helmet mounted raster type projector. In even greater particularity, the present invention may be characterized as a rapid head movement compensation device for offsetting a raster scan during movement of the projector.
2. Description of the Prior Art
Simulator devices for pilots and vehicle operators have always been lacking in dynamic presentation of visual input to the trainee, particularly where wide angle displays are concerned. The best current approaches for wide angle displays involve the use of multiple computer generated imagery channels and associated projection equipment to provide imagery for individual parts of the viewing area. These individual fields of view or windows are butted together to form a continuous wide angle display. Obviously such a display requires substantial investment in material and maintenance.
A way to reduce the economic impact by reducing the number of CIG channels and associated projection equipment is to project video imagery from the viewer's helmet onto a large spherical dome screen of retroreflective material. Positional outputs from head and eye trackers are used to determine the viewer's look direction and the CIG system provides images in accordance with the determined outputs.
As an added benefit, mounting the projector on the helmet of the viewer reduces perspective distortion by locating the projector exit pupil close to the eye of the viewer, thereby decreasing the software and hardware development required to correct for the distortion, and correspondingly reducing the image computation time associated with distortion correction.
Unfortunately, there are time delays associated with both the determination of the viewer's look direction and the subsequent mathematical modeling of the image for projection by the CIG system. Using a 60 Hertz CIG update rate, it can be expected that the projected image will lag the motion by at least 85 to 90 milliseconds, thus the details of the viewed image will appear to swim or reposition themselves at the end of a head movement. The effect of having stationary objects, such as trees, appear to jump obviously detracts from the training effort.